Process of electroforming thin walled tubing



July 4, 1967 N. B'. MEARS 3,329,588

PROCESS OF ELECTROFORMING THIN WALLED TUBING Filed Aug. 28, 1965 STEP I COAT PLASTIC THREAD WlTH SILVER BY SPRAYING STEP 2 INVENTOR L Ill NORMA/V B. MEA/PS CUT TO LENGTH, STRETCH BY M AND PULL OUT THREAD ATTORNEY United States Patent Office 3,329,588 Patented July 4, 1967 tion of Minnesota Filed Aug. 28, 1963, Ser. No. 305,042 9 Claims. (Cl. 204-9) This invention is directed toward a process for forming miniature, hollow, very thin walled metallic tubing.

To set this invention in its proper environment, tubing formed according to the teachings of this invention have dimensions in the range of .005 inch inner diameter with an outer diameter in the range of .007 inch. It should be understood, of course, that these dimensions are only illustrative of the small dimensions involved and not intended to be limitive. Tubing of this nature has been required in certain miniaturized equipment and can be produced economically in quantity according to the present invention.

The drawing illustrates in three views, three steps in the process of forming the thin walled tubing.

Referring to the accompanying drawing which illustrates the step-by-step process of this invention, a continuous thread 10 of elastic material is unwound from reel 12 and passes through a spraying station 14 Where a very thin coating or layer of metallic material is formed on the thread in step 1. The coated thread then passes via an idler take-up reel 16 into a suitable electrolytic bath, indicated at 18, wherein a thin covering layer of metallic material is plated by electro-formation on the coating layer in the second step. After the covering layer of metallic material has been plated to the desired thickness, the nibular product is cut into predetermined lengths, as indicated at 20. The product thus formed comprises an elastic thread core 10, a coating layer 22 and a covering layer 24. The thread core is then removed by stretching it longitudinally so that its diameter decreases along its length separating it from the coating layer and the thread core is thereupon pulled out leaving a fine tube of metallic layers as illustrated at 26.

Preferably the thread is plastic such as a relatively soft polyethylene material which is stretchable and deformable. A suitable thread material is produced by E. I. du Pont de Nemours & Co., Inc. under the internalcode designation of 3HA, color NC 10*, and is typically of a diameter in the range of .003 to .005 inch. Other suitable thread materials having the required characteristics may be utilized under the teachings of this invention and the foregoing Du Pont product is only intended to be illustrative and not limitive.

The spraying procedure in step 1 is preferably in accordance with what is referred to as the Peacock silver spray process. This spray process is generally as described in Patent No. 2,214,476 and briefly comprises the steps of spraying two solutions, one of which is a silver nitrate solution and the other of which contains a reducing agent, concurrently onto the plastic thread. When the solutions impinge upon the thread the silver is chemically reduced out as a thin coating on the thread. The spraying can be controlled to a high degree of accuracy to limit the coating layer to a very thin film in the order of .00005 inch thick. When sprayed on in this manner, the silver coating is deposited chemically in contrast to the other known methods of deposition. The thin silver coating serves a two-fold purpose. One is that it adheres to the plastic thread with suflicient strength so as to adequately serve as a conducting electrode for the subsequent deposition of the additional metallic covering layer by electrolysis, but on the other hand the degree of adhesion to the plastic thread is sufficiently low so that the thread can be subsequently readily separated and removed without damaging the covering layer.

The electroformation of the covering metallic layer, which provides structural strength for the tubing is accomplished in the well known manner. As previously stated, the silver coating layer has sufiicient conductivity so that the metallic covering material, such as nickel or copper, will be readily placed thereon by electrolysis. Typically, when plating with nickel the anode in the bath is nickel and the bath, commonly referred to as the Watt bath, consists of suitable nickel content, chloride content and boric acid having a pH in the order of 4.75 at a temperature in the range of 114 to 117 F. Appropriate materials to the required percentages at proper temperature, etc. for proper electroformation are a matter of choice and design and those of ordinary skill in the art canreadily determine suitable requirements for the bath depending upon the material to be deposited during electroformation, the thickness of the plating, etc. The above listed contents for the electrolytic bath are obviously only illustrative and not limitive. Typically the coating layer of metallic material is deposited to athickness in the range of .001 inch.

After the electroformation procedure the tubular prodnot so formed is cut into appropriate lengths, typically in the order of sixteen inches. The ends of the thread core of the respective lengths are grasped firmly and the thread is longitudinally stretched to a degree sufficient to reduce the diameter of the thread along its length to separate the thread from the coating layer of silver. As previously stated, the strength of adherence of the silver coating to the thread is suificiently low, as compared to the strength of adherence of the silver coating to the covering metallic layer, that this step in the process is readily accomplished. The thread core is then removed by pulling it out leaving an elongate hollow metal tube.

It will become obvious to those of ordinary skill in the art that under the teachings of this invention there is a variety of materials which can be used as the plastic thread care, as the thin coating film to serve the dual purpose described hereinabove and as the coating material, with the accompanying advantageous features provided by this invention.

It is apparent that since the equipment and procedures described herein for accomplishing the process of this invention are readily obtainable and knowledgeable, that this invention is adaptable to economic implementation into a facility for producing the hollow thin walled tubing in the manner described so that tubing can be produced in quantity at an economical cost.

I claim:

1. A process for forming thin wall metal tubing comprising the steps of:

(a) forming a thin coating layer of metallic material on an elongate plastic thread;

(b) plating a thin covering layer of metallic material on said coating layer by electroformation; and

(c) pulling out the plastic thread whereby an elongated hollow tube is formed.

2. A process for forming thin wall metal tubing comprising the steps of (a) spraying metallic material on an elongate plastic thread to form a thin metallic coating layer thereon;

(b) eleotroforming a thin covering layer of metallic material over said coating layer; and

(c) longitudinally stretching the plastic thread to reduce its diameter along its length and pulling it out whereby hollow metallic tubing is formed.

3. A process for forming a thin wall metal tubing comprising the steps of:

(a) forming a thin coating layer of a first metallic material on an elongate plastic thread by spraying;

(b) plating a thin covering layer of metallic material different from said first material on said coating layer by electroformation; and

(c) then longitudinally stretching the plastic thread to reduce its diameter along its length so that it separates from the coating layer, and pulling the thread out whereby an elongated hollow tube is formed.

4. The process as described in claim 3 wherein the plastic thread is stretchable and deformable polyethylene.

5. The process :as in claim 4 wherein said first metallic material is silver.

6. A process for forming thin wall metal tubing com prising the steps of:

(a) passing a continuous elastic thread through a spray of metallic material forming a thin metallic coating layer thereon;

(b) passing the coated continuous thread through an electrolytic bath plating a thin covering layer of metallic material over said coating layer to form continuous tubing;

(c) cutting the tubing to predetermined lengths; and

(d) stretching the thread in the respective tubing lengths to reduce the. diameter thereof along said lengths and pulling the thread out of the covering layers thereby forming elongated hollow tubing.

7. The process as in claim 6 wherein the thread is stretchable and deformable polyethylene.

8. The process as in claim 7 wherein the elastic thread is sprayed with silver in step (a).

9. A process for forming thin wall metal tubing comprising the steps of:

(a) forming a silver coating in the order of .00005 inch thick on an elongate thread of stretchable deformable polyethylene in the order of .005 inch diameter by spraying;

(b) plating a covering layer of metal selected from the class consisting of nickel and copper in the order of .001 inch thick on said coating by electroformation;

(c) stretching the thread to reduce its diameter along its length so that it separates from the silver coating and pulling out the thread whereby an elongate hollow Within the metallic layers is formed.

References Cited UNITED STATES PATENTS 473,732 4/1892 Elmore et al. 204-25 666,321 1/1901 Langh ans 204-290 1,023,612 4/1912 Bensinger 204-9 1,544,856 7/1925 Murray 249-183 2,181,256 11/1939 Arbogast 204-281 2,768,133 10/1956 Lundbye 204-20 2,949,410 8/1960 Bingham 204-9 2,967,805 1/ 1961 Forestek 204-20 FOREIGN PATENTS 757,539 9/1932 France.

JOHN H. MACK, Primary Examiner.

W. VAN SISE, Assistant Examiner. 

1. A PROCESS FOR FORMING THIN WALL METAL TUBING COMPRISING THE STEPS OF: (A) FORMING A THIN COATING LAYER OF METALLIC MATERIAL ON AN ELONGATE PLASTIC THREAD; (B) PLATING A THIN COVERING LAYER OF METALLIC MATERIAL ON SAID COATING LAYER BY ELECTROFORMATION; AND (C) PULLING OUT THE PLASTIC THREAD WHEREBY AN ELONGATED HOLLOW TUBE IS FORMED. 